Friday, February 04, 2011

Project Coordination - Early Days

This post attempts to outline how a project will develop (understanding there are exceptions) when considering multiple firms/models and attempting to keep each model aligned both in Revit's model environment and relative to the site location and survey information. It differs from previous explanations I've offered here because the separation of models tends to challenge the traditional Publish and Acquire Coordinates tools. These tools work more readily when all the models co-exist on the same network, shared among the team. Less so when that isn't possible.

In the beginning..."You" (an architecture firm) start your project without a reliable survey. Sometimes the survey is a hand drawn document from a "couple years ago" or it's just a legal deed description. Maybe it is just from a survey you don't trust? Regardless you are less than excited about relying on it completely. Someone arranges for a survey or less convincingly...one is being promised.

Using a new project template (your killer office template of course), start your Revit project at (near) the origin in Revit (project basepoint). Don't even worry about the survey information for the moment. Draw the concept so it is easy to put on paper, on a printed sheet. Doesn't matter if it is angled or new fangled, just orient it so it is "easy" to draw.

When the survey comes in or you are forced to do some site documentation (guessing) create a new Revit project file (for example call it: Site Master or Master Site) and create whatever information you intend to use in this file. The presiding reason to create this separate file is to minimize the pain and suffering should the building location change or if there is more than one building involved. Work in this file, orienting everything with North as the top of the view, North is "UP" (like World Coordinates "WCS" in AutoCAD).

You also need to match the coordinate system of the Master Site Revit project to the survey. The most reliable way to do this is to agree on a benchmark location in the survey and use those values with the Specify Coordinates at Point tool to define that same spot in Revit. The reason it is most reliable is that large coordinate values do not get extracted properly using the Acquire Coordinates tool. Safer to use the one that "always" works, I think. When the survey is imported into Revit use Auto-Center to Center so that it is near Revit's own origin. Then the Specify Coordinate at Point tool will adjust the Survey Point to indicate where the survey 0,0,0 (origin) is. If you "un-clip" the Survey Point first you can use it to mark the benchmark and it won't shift to mark the survey origin.

Now that this file exists you have some understanding of the site and hopefully have an idea about where the building ought to go. Import your building model using Manual at Origin and "plop" your building somewhere on the site. Move it into position, align/rotate it and raise it to the ideal ground floor elevation (literally move it up/down in a section or elevation view). Once the building is where you believe it should go you can define the important site information to share with everyone else. Contrary to typical convention don't bother with Publish Coordinates. More on this in a bit, hang in there.

Let's pause, back up and insert some stuff between the building model and the site model coming into being, before you get reliable site information (or faking it).

Let's assume you decide to hire a structural engineer (and MEP) and they use Revit too. You send them a copy of your model (remember, before any notion of real site position information). They import your model Auto-Origin to Origin. The reason for this is that the extent of your model is likely to be different than the extent of their template. Using Auto-Center to Center will not guarantee that your origin and their origin are at the same place. You want the Project Base Point (Revit's project origin) to be the same in both files. The MEP consultant does the same. The engineers match up their levels and grids to yours using Copy/Monitor (most likely...or probably should).

At this point everybody has models that are at the same location from one Revit file to another. Importing any file into another will end up at the same spot in each other's file. If you never deal with site you are all good to go.

If we assume that you and the engineers have traded files a few times we can reconcile the site conditions when they become available. When a real survey exists (or even a fake, good enough for now one does) you add it to the site master file and use it to define (as described earlier) the actual coordinates so the master site model and the civil information are in sync. Assuming you have to adjust the building you do it here, in the Site Master file. Move it, align/rotate and raise/lower it but as I mentioned before, DON'T bother using Publish Coordinates.

When you are passing models back and forth the process (FTP/Uploading/Downloading) of publishing coordinates breaks down if/when your architecture model has to be moved on the site. The relationship between the site and your model is easy. Not so easy for the other models and your model to say in sync. The goal should be to keep the project origin intact between files. Instead of Publish Coordinates, we will use the Specify Coordinates at Point tool to tell each project file what the site information is. This is done by determining what the necessary information is in the Site Master file and passing it along to each team/model. It's a simple list: East/West & North/South Coordinate for a established location like Grid intersection A1, Elevation at that location and the building Rotation relative to East or West. It looks like this when you've got it entered into a building/structure/mep model.


You extract this information from the Site Master file by using the Report Shared Coordinates tool at Grid Intersection A1 (or something agreed upon). This gives you the E/W and N/S coordinates and the Elevation. Rotation is determined by finding the angle between True North and the Grid (or something) that represents Project North.

As mentioned above, you don't actually publish coordinates or acquire them. You use Specify Coordinates at Point in each model to tell Revit what the real world coordinates are at that point (Grid A1), what the elevation of the project is and what the rotation of the project is. As soon as you enter the information Revit "adjusts" the project but it never really moves. All the project views are intact. The only time that major changes are required by everyone are when the model itself is redesigned to different angles or shapes. It's hard to avoid that kind of rework. Repositioning the building on the site however is updated with much less trouble or downstream heartache.

You just repeat those steps if the site conditions or something forces a change and pass the new coordinates, elevation and rotation information along to the engineers. They use Specify Coordinates at Point, enter the data...back in sync. If they don't update the information the models still stay in sync between Revit files. The failure to do so only becomes apparent when the model is exported to Navisworks or a cad file for Civil to use.

In a flow chart the concept looks like this.


The coordinate data in the dashed boxes could be as simple as four lines in an email, like this:

The new project coordinate information is a follows
  • E/W Bearing: 1,500,000
  • N/S Bearing: 1,250,000
  • Elevation: 142'-0"
  • Rotation: 25 degrees Relative to: West

If there are multiple buildings involved the process is the same except they'll each have their own unique coordinate information ultimately derived from the building model located in the Site Master file.

This is my first pass at documenting this...so if I've missed something or described it poorly...I'll be back. I'm also planning on a video capture or two...

18 comments:

David Light said...

Excellent post Steve, I have read it a couple of times and it's certainly clear to me. To some extent this is how I use to do the process in autocad although setting the ucs was a little easier, but then you are achieving the same result of a common shared coordinate location by specifying a coordinate at a point.

hoogli said...

great post, just going thru this with a client but to far into the process. needed this chart at start of project.

Anonymous said...

Excellent post. Very clear. However we always use shared coordinates for linking consultants revit/cad files, instead of origin to origin. We also use shared coordinates during 2D dwg export from revit.

Steve said...

Thanks. I wrote that late at night so I wasn't sure I was coherent!

Anon... your comment suggests to me that you don't see the difference between what I wrote and using "shared coordinates". You can't use shared coordinates between files when you import them if there are no shared coordinates to import with.

Two Revit project files that are linked origin to origin...don't "need" shared coordinates and Revit will generate a warning saying that there are none.

The purpose of establishing a common coordinate and orientation isn't for the Revit project file relationship, it's for external relationships (and so you can show a site orientation inside Revit documentation).

My post doesn't get into the export process but it is important to export using the Shared option instead of Project.

Perhaps your comment was just quick and didn't fully express "how" you tackle this stuff?

Erik van Eck said...

Excellent post Steve!

Groet Erik

hanap said...

Wow, this is excellent - you saved me today!

Anonymous said...

I work at an MEP firm and we use "Auto-By Shared Coordinates" positioning when setting up our models.

The architectural model is linked into our MEP project template file (we use a template Revit project, not a Revit template) using "Auto-Center to Center" (this is just to get it into our model). Beings that the Architectural model is the significant model as far as the location is concerned, we Acquire Shared Coordinates from the architectural model. This modifies my MEP model so it has the same shared coordinate system as the architectural model and it also sets true North (assuming the architect got it right in their model).

The structural model is then linked in (again the method of linking doesn't matter because i will be using shared coordinates in a bit) and the model is aligned to the architectural model using grids and levels. The coordinate system of my project is then published to the structural model. This process is repeated for any additional models we receive.

I have now acquired coordinates from the architectural model into mine (making the architectural and my MEP model have the same shared coordinate system) and published coordinates from mine to the structural (making the architectural, structural, and mine have the same shared coordinate system). All models share the same coordinate system and by using shared coordinates I am protected from the architect or structural engineers moving their models (yes this does happen). If they do chose to move their models, the change in location doesn't move there models in mine because the shared location is the same in all models.

This method is fewer steps than that listed above and allows for more flexibility moving forward by allowing for the creation of multiple locations for a building or linking multiple buildings into a site plan with defined locations for each.

See the link below for Autodesks description of when to use shared coordinates.

http://wikihelp.autodesk.com/Revit/enu/2012/Help/Revit_User's_Guide/2214-Collabor2214/2408-Shared_P2408#WS46B90C3CB2C58CAD197A37CFC7FA555F3-8000

Chris Heinaranta said...

Thanks Steve,
we're using this on a project. Just a note, since the "point" you specify is 3D you should be aware of how your going about to establish it.

We started with intersecting reference planes and found out our elevation was off. We figured out the cut plane comes into effect, so we set it to 0. To be extra paranoid we drew a model line from the intersection of the reference planes and used the end of the model line to establish our common point.

Also be consistant on what level you use. Our main floor was the common level to be used throughout all the files.

Steve said...

Good comments Chris. Yes the Specify Coordinates at Point tool does pick up the elevation value of the point. My post does tend to favor those with a bit of experience with this stuff already.

Not specifically responding to Chris, technically this whole post is irrelevant if the other trades don't have to export for alignment in other systems. If that's really true then starting out with placement using Auto - Origin to Origin is all that's required to keep everyone aligned with one another.

If the building elements are actually moved to new positions in the architectural model it will end up "wrong" in the other models it shows up in. For example, a building getting a bit wider or longer will require all the other trades to adjust their designs to deal with the new dimensions.

The approach described in my post is very reliable for dealing with buildings that are reoriented on site. Such as those that were parallel to a road and then rotated to align with some other feature. It's easy (almost trivial) to rotate a model in the master site model.

It's much harder to do that in the building file itself. Such a change need not affect the rest of the trades at all, and doesn't with my approach because the only thing that actually changes is the survey point coordinate data, not the building itself.

I think it's important to stress that the change(s) I'm writing about managing are quite different from changes to the building itself, it's shape, dimensions or concept.

PLawton said...

Sir:

Not to be a sharpshooter, but using Revit MEP 2012 (and earlier) we get error messages complaining about the site being 'larger than 20 miles' ... your example is closer to 200 miles. Does this cause any pains downstream?

Thanks

Steve said...

Revit doesn't mind the large coordinates. It doesn't like geometry that is very large or very far from it's own origin. Supplying the real world coordinates for the site to a project that exists within the 20 mile boundary is no problem.

Revit is just transposing the "local" coordinate value to the "global" real coordinate value. Imagining a conversation within Revit, "Oh, so coordinate 10,20 is really 11,550,15,500? Thanks for letting me know!"

XeroPhane said...

I realise this post is over a year old but it's still very relevant. I just had a contractor seriously upset that our Revit models were all over the place when he imported them into Navisworks (thereby disrupting his site robotics, forms, etc)... Our models used the Publish/Acquire coordinates system that obviously failed miserably, or at least crumbled to bits within Navis. I needed something from an outside source to illustrate my proposed remedy and this fit the need perfectly. Thank you!

mamiller said...

Thanks for this post Steve.
I'm starting a new project and was trying to wrap my head around Shared Coordinates, which I've never fully understood. I had been trying to figure out how to setup shared coordinates on a project so that the consultants could acquire the coordinates the coordinates for their models and I couldn't figure out how to publish coordinates without having control of the consultant's models. this helped out a lot in understanding the proper work flow.

Benjamin Dover said...

This is an old post but very useful. Thank you!

I have successfully set up the shared coordinates between my models, however our office standard is to show the project datum (main floor) = 100000(mm). Once I established the shared coordinates, all my models now report the main level at 0.

How can I change this such that the true geodedics are preserved but the project datum is from 100000?

SkyC said...

Steve, I'm having a bit of trouble getting this right. I have my separate building files and site file set up. I have gotten a basepoint from civil and specified it in the site file. I have placed my buildings and have reported the coordinates at the A/1 grid for my individual buildings from the their position in the site file. I have then gone into the individual building files and specified those exact coordinates at their respective A/1's.

SO - now when I link the site into my building files using OTO, the site file does not show up in the right spot - way off. Same thing when importing the site CTC.

What am I missing? Any help would be appreciated. Thanks.

Steve said...

SkyC - when you establish shared coordinates you use "Auto - by shared coordinates" instead.

SkyC said...

Thanks for your fast response - I have tried that but get the message that "the document and the imported instance do not have the same coordinate system - CTC will be used".

So even though my A/1 coordinates for the building as positioned in the site model and the A/1 position in the building model are exactly the same, Revit still thinks they are not on the same coordinate system. Strange.

I am assuming there was no point along the way where I should have published or acquired coordinates according to your article.

Not sure if this helps narrow down what the problem is? Thanks for your help.

Steve said...

Sorry the delay, I've been traveling and then out sick :(

When you choose by Shared Coordinates and the files are not sharing coordinates Revit will report that as you say but it also says something else significant...

that it will use the WCS of the project which means the same shared coordinate values thus they will line up, or at least they should unless something has changed since I wrote all this.

I'll have to double back and test it all again with 2014.